Meghan van Aarde’s recent coughing fits kept her awake at night, left her gasping for breath and even interrupted her classes at California’s Whittier Law School.

“It got to the point where I’d have to leave class. I knew I was disrupting other people,” van Aarde, 30, said.

Doctors blame pertussis, commonly known as whooping cough, for a spike in hacking fits nationwide.

Despite decades of vaccinating children against pertussis, cases of the potentially fatal infection are at a 45-year high. Pertussis has been linked to the deaths of six California infants in 2005 and is the only contagious disease on the rise despite the availability of a routine vaccination for children.

An immunization advisory committee at the Centers for Disease Control and Prevention recently expanded its recommendations for the pertussis vaccine to all adults. The vaccine is being added to the tetanus-diphtheria booster shot for adults and already has been recommended for adolescents. Pertussis immunization wears off about five to 10 years after children receive their last vaccine between the ages of 4 and 6. About 60 percent of those infected with pertussis are teenagers or adults, researchers say.

While pertussis is usually not serious in adults, it can be fatal to infants who have not received the full course of five doses.

There were about 26,000 reported cases of pertussis in 2004, the highest total since 1959. Experts do not know the reason for the increase, but suspect that more accurate diagnosing is partly responsible.

Pertussis is difficult to diagnose because its initial symptoms – low-grade fever, runny nose and cough – mimic a cold, allergies or bronchitis. Research has indicated that some 97 percent of cases may go undiagnosed.

“I’m so concerned about the spread of pertussis,” said Dr. Brian Levine, who treated van Aarde at the newly opened Cough Center in Mission Viejo. “We’re treating adolescents and adults, but really it’s a concern for mortality of infants under four months.”

Levine founded the Cough Center to diagnose and treat whooping cough and chronic coughs caused by allergies, asthma or other illnesses. Patients with coughs often overlook the symptom or don’t know which type of doctor to see, Levine said.

Family members infected with untreated whooping cough can be blamed for 75 percent of pertussis cases in infants. The National Association of School Nurses launched a campaign in August encouraging older children to get pertussis booster shots.